What makes a good activity

Please, reflect back on your time as a student and a teacher and find an activity that you thought worked really well -- a moment when important learning was taking place. What was it about that activity that made it work?

Please share an aspect that made your activity work. If you could read the posts ahead of yours and try to add something to what has already been said, either a new idea or an expansion on an idea already presented- then I think we will generate a pretty good list.

The activity that comes to mind for me is a really simple one that I learned very early on in college and have used at all levels of outreach activity since. It is a variation on the cloud in a bottle experiment, including a thermometer and a "fizz-saver" pump. For those of you who don't know it - by placing a little water in the bottom of a two liter bottle, then introducing a little smoke from a blown-out match, then pumping up the pressure inside bottle and releasing that pressure suddenly so the air inside the bottle cools down and net condensation occurs forming a cloud.

This is an activity with huge learning potential. I always ask my students what they expect before we do anything. I review basic ideal gas law physics by monitoring how the temperature in the bottle changes as the pressure changes. I do the demo once without smoke and ask the students afterward why they thought the smoke made a difference. I've even done it by asking students to plot the changes in temperature inside the bottle (it would be nice to computerize it sometime I think, but that adds lots of expense).

Bottom line? Making it into an experiment, complete with hypothesis testing, data plotting, asking the students to draw conclusions, and then discussing those conclusions. All age groups get something out of this demo, depending on what questions you ask. And it's something students can do themselves. That's what makes this activity work in my opinion.

I need to keep this short as I am about to run off to class, but I think that in any activity I do in class - whether it's an activity that spans several class periods, or one that takes 5 minutes, a key factor is that every student needs to have a 'role' - every student needs to feel that they are contributing - to their own learning, and to that of their classmates - either through discussion, as a note-taker, as an experimenter, etc... Group activities where duties can be subdivided seem to be some of the most successful...

In my experience, the simpler the activity the better. I certainly don't remeber any of the complicated physics labs I conducted in college but I do remember by professor spinning on a stool pulling his arms in and out. The other thing I've learned is to make ONE point with an activity. JUST ONE!!!!!

Todd: I do the cloud-in-a-bottle demo that you describe a lot, though the version without smoke initially is a nice variation that I haven't tried yet on students. I've often thought wistfully about how nice it would be to be able to measure the temperature and pressure inside the bottle during the experiment, to verify the claims I make about those quantities before and after releasing the stopper on the bottle. Do you know of (relatively cheap) ways to measure those things and make the measurements accessible to a classroom of students?

By the way, as a valuable adjunct to the standard cloud-in-a-bottle demo, I precede it with another demo. I commute to campus by bike, so I remove my front wheel, grab the hand pump attached to the bike, and bring them to class (along with a thermometer and the bottle and matches). You can guess what I'm going to do with the bike wheel, I'm sure, but here's the procedure that I use, roughly:

(1) Have several students feel the metal valve attached to the bike tube, and comment how warm or cold it feels.
(2) Give a student a thermometer and ask them to measure the room temperature. [Ideally I'd have a fan available. I'd turn it on and ask students to predict what will happen to the temperature measured by the thermometer if it's stuck in front of the fan. Although there's no significant change in temperature, the result tends to be counterintuitive for some students and can lead to a lengthy though interesting diversion about how thermometers work and what they actually measure--namely, their own temperature.]
(3) Ask students what they think the pressure is like inside the tire, compared to the pressure outside the tire. Tell students that I'm going to open the valve on the bike tube, whereupon the pressure difference between the inside of the tire and outside should push air out of the tire, and as air comes out of the tire the pressure on that air should decrease. I ask students to predict what, if anything, should happen to the volume (or density) of the emerging air as a result of the pressure decrease, and what might happen to the temperature of that air as a result. [They've had a reading assignment beforehand that should allow them to predict this.]
(4) Ask a student to hold the thermometer directly in front of the valve without touching it, and open the valve. Air streams out for a few seconds. Ask the student to read the thermometer. Ask the students who had felt the metal valve beforehand to feel it again and comment on the difference. Ask the thermometer-reader to comment on the observed temperature change, if any. [Can constrast this to results of putting thermometer in front of the fan earlier, if that was available.] [This might raise questions about why the valve cools off if it's air that is supposed to cool when the pressure decreases. With prior reading, some of them can identify the relevant process as conduction.]
(5) Summarize results of this experiment: when the pressure on air decreases, the air expands and cools.
(6) Commenting that repressurizing the tire is necessary so that I can get back home at the end of the day, I reverse part of the experiment by pumping air back into the tire, noting that pushing on the pump plunger puts pressure on the air inside the barrel of the pump, which compresses that air. Also, the pressure inside the pump becomes greater than the pressure inside the tire, and the pressure difference pushes air from the pump into the tire. I ask students what should be happening to the pressure inside the tire as a result of pumping more air into it. Pumping air into the tire warms me up quite a bit--those small hand pumps are a lot of work. It also warms up the barrel of the small pump, as students can verify by touching it. The same is true for the tire valve. Conclusion: Increasing the pressure of air compresses it and warms it up. [They might argue that friction of the plunger against the inside walls of the pump generates heat and is responsible for the warming of the pump and the pressurized air. I can't disprove that, so what I sometimes do is deflate the tire before class and do the repressurizing experiment first, let the air inside the tire and the valve cool to room temperature [this happens pretty fast], and then ask students to predict what will happen to the temperature of the air and valve when the valve is opened and air rushes out of the tire. Any predictions based on friction will fail, and the available alternative hypothesis (temperature changes result from changes in volume caused by changes in pressure) will prevail.
(7) During the cloud-in-bottle experiment, I ask several students to take turns pumping air into the bottle using the compressible bladder attached to the bottle stopper. [It gets progressively harder to compress.] I ask them to comment on what this might tell them about what is happening to the pressure inside the bottle. Then I ask them to predict what will happen to the pressure inside the bottle when we pop the stopper, and why, and predict what will happen to the temperature as well. [These are the changes I haven't figured out how to measure directly.]

Julie Snow points out the merit of making just one point with an experiment, and the cloud-in-a-bottle demonstration, which is very dramatic and the students love it (as do the 5th and 6th graders through high school students for whom I've done it) makes this a little difficult--there are several important physical principles at work, almost all of which we typically try to teach students in an intro meteorology class. Doing the bike tire demo first helps separate the points about pressure changes causing temperature changes from the point about temperature decrease leading to condensation in the form of a cloud (and the role of condensation nuclei--the smoke from the match), which helps, but there are still several points that each demo makes.

The compromise might be simply to take the time needed to make each point clearly--rushing them will likely cause confusion.

Using this thermometer, you can qualitatively see the temperature increase, and I think you can buy that kind of thermometer for 3-5 bucks and while it's not terribly accurate, it's easy for many students to see even from a distance. To be more quantitative, might require a bit more engineering. I've been dreaming about how to do this, but so far the dreams are just that.

And Dave, I agree with your point about multiple points - there are just so many good things about this demo. I often rely on the fact that most students have had high school chemistry and so the pressure/temperature relationships are often review (though mentioning Ideal Gas Law sometimes invokes mild twitching from some students...)

For measuring the temperature in the cloud in a bottle experiment I simply hang an aquarium thermometer (like this one: http://www.aqua-fish.net/imgs/articles/aquarium-thermometer.jpg) in the bottle. I use a piece of scotch tape a couple of inches long that I tape one end to the thermometer and the other end in the inside of the bottle to allow the thermometer to hang freely. Then when you pump in air you can see the temperature rising on the thermometer and falling when the air is released. You can not get very precise measurements but you can get some values and can very clearly see the relative change. (The students can also feel the pressure increase as it becomes harder to squeeze the bottle.)

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